Ethernet (registered trademark) is one of Local Area Network (LAN) Standards. The Ethernet (registered trademark) is the LAN connected by cables and is used for establishing connections between personal computers (PCs), a server and network devices. Recently, the LAN is frequently used for connecting household electrical appliances such as game machines and TV systems to a network.
Further, recently a wireless LAN such as Wi-Fi (registered trademark) is also frequently used for establishing connections between the network and a variety of electronic devices such as mobile phones, smart phones and portable game machines in addition to the PCs and Personal Digital Assistants (PDAs).
Thus, protocols based on the Ethernet (registered trademark) and the wireless LAN is protocols taking charge of a data link layer defined as a second layer (Layer 2) in an Open Systems Interconnection (OSI) reference model.
FIG. 1A is an explanatory diagram of a frame format of the Ethernet (registered trademark), and FIG. 1B is an explanatory diagram an IEEE802.3 frame format. FIG. 1C is an explanatory diagram of an IEEE802.3+802.2(LLC) frame format, and FIG. 1D is an explanatory diagram of an IEEE802.3+802.2(LLC+SNAP) frame format. Thus, the frame format of the Ethernet (registered trademark) and the IEEE802.3 frame format have several variations including the frame formats illustrated in FIGS. 1C and 1D as a result of extensions. It is, however, common among all the frame formats to use Media Access Control (MAC) addresses as a source address and a destination address.
In the present specification, the network of Layer 2 using the frames as depicted in FIGS. 1A-1D will hereinafter be called the “LAN” or a “wired LAN”, and each of the frames used in the LAN will hereinafter be called a “MAC frame”.
On the other hand, the wireless LAN also has the same frame format as the format of the MAC frame. FIG. 1E is an explanatory diagram of the frame format of IEEE802.11 defined as the LAN Standard for the wireless LAN. The format illustrated in FIG. 1E has four address fields. A value stored in each address field varies depending on a combination of the wired LAN and the wireless LAN in a network configuration (topology). The frame in the wireless LAN will hereinafter be called a “wireless LAN frame”.
FIG. 2 is an explanatory diagram of designating the address field of an IEEE802.11 header in a case where a wired section and a wireless section are connected to each other. In FIG. 2, the wireless section is provided between a wireless LAN terminal and an access point (AP), and the AP is connected to the network to form the wired section.
When a frame is transmitted from the wireless section to the wired section (a wireless LAN terminal−>an AP), as illustrated in an example of FIG. 2, Basic Service Set Identifier (BSSID) is set in a first address field (Address 1) of the IEEE802.11 header of the frame. The BSSID is one of network identifiers based on IEEE802.11 and corresponds to the MAC address of the AP. The MAC address of the wireless LAN terminal is set as a MAC source address (MAC-SA) in a second address field (Address 2). The MAC address of a destination of the frame is set as a MAC destination address (MAC-DA) in a third address field (Address 3). There is no address to be set in a fourth address field (Address 4).
On the other hand, when a frame is transmitted from the wired section to the wireless section (an AP−>a wireless LAN terminal), the “MAC-DA” (the MAC address of the wireless LAN terminal) is set in the first address field of the IEEE802.11 header of the frame, and “BSSID” (the MAC address of the AP) is set in the second address field. The “MAC-SA” is set in a third address field. There is no address to be set in the fourth address field. As illustrated in FIG. 2, in the wireless LAN, the MAC addresses are used as the source address and the destination address.
Incidentally, the Internet is one of networks which is widely used at present. The Internet is a network adopting an Internet Protocol (IP) as a protocol for a third layer (Layer3), i.e., a network layer in the OSI reference model. The IP protocol is classified into IPv4 used from the beginning and IPv6 developed for solving a depletion issue of the IPv4 address.
The Internet is explained as “a network of networks” as the case may be. This implies that “the Layer3 network is a network to interconnect the Layer2 networks”. The Layer2 network is different from the Layer3 network.
The IP protocol is originally a protocol developed for the Internet. Recently, however, the IP protocol is diverted to private networks, enterprise networks (Intranets), etc., which are not connected the Internet at a Layer3 (L3) level. Further, such a point is reached that the IP protocol is utilized on in-home networks. In the present specification, the network utilizing the IP protocol is called an “IP network”. The wired LAN and the wireless LAN described above are generally used on the IP network represented by the Internet. An IP packet forwarded via the wired LAN is encapsulated with a MAC frame (a frame based on IEEE802.3), while the IP packet forwarded via the wireless LAN is encapsulated with a wireless LAN frame (a frame based on IEEE802.11).
An extended technology called Virtual LAN (VLAN: IEEE802.1Q) is exemplified as a technology related to the LAN. The VLAN is used for forming logical networks on a physical network(s). For example, the VLAN is used in the case of segmenting a physically shared network on a predetermined management unit and managing the segmented networks per management unit. Alternatively, the VLAN is used to multiplex (accommodate) a plurality of IP networks employing IPv4 private addresses on the same physical network.
FIG. 3A is an explanatory diagram of a format of an IEEE802.1Q frame. The format of the IEEE802.1Q frame is formed by adding a VLAN Tag field (TAG: 32 bits) to an Ethernet (registered trademark) frame. It is feasible to distinguish among 4,094 VLANs at the maximum by use of a VLAN Identifier field (VID: 12 bits) in the VLAN Tag field.
Classically, the VLAN was used for segmenting the LAN into a plurality of management units to operate the LAN at the management unit. Thereafter, the VLAN is used for providing wide-area LAN services for establishing connections between the LANs each of which is in a plurality of base points. Main users of the wide-area LAN services are enterprises having a plurality of base points and an intra-network, and generally private addresses are employed in the intra-network. Therefore, the VLAN (VID) being different per intra-network is allocated even in an environment where the same IP address is utilized for the different enterprises, thereby enabling intra-networks to be logically distinguished from each other.
Recently, the VLAN is increasingly utilized to build up infrastructures for data centers and cloud services. Especially, when hosting relating to user networks (e.g., enterprise systems) is performed, the same address is used within the different enterprises similarly to the wide-area LAN services as the case may be. In this case, there is a merit that a network can be logically segmented (divided) by the VLAN technology (the users (networks) are identified by VIDs).
For more information, see International Publication Pamphlet No. WO2001/099354